The present invention relates to dithienobenzo-thieno[3,2-b]thiophene-copolymers and their use as high performance solution processable semiconducting polymer.
The formidable building block for the development of (micro)electronics during the second one-half of the 20th century is the field-effect transistor (FET) based on inorganic electrodes, insulators, and semiconductors. These materials have proven to be reliable, highly efficient, and with performance that increases periodically according to the well-known Moore's law. Rather than competing with conventional silicon technologies, an organic FET (OFET) based on molecular and polymeric materials may find large scale applications in low-performance memory elements as well as integrated optoelectronic devices, such as pixel drive and switching elements in active-matrix organic light-emitting diode displays, RFID tags, smart-ID tags, and sensors.
As a result of the development of several conductive or semiconductive organic polymers, the application of those as active layer, thus the semiconductor, in organic thin-film transistors (OTFTs) has gained increasing attention.
The use of organic semiconductors in OTFTs has some advantages over the inorganic semiconductors used to date. They can be processed in any form, from the fiber to the film, exhibit a high mechanical flexibility, can be produced at low cost and have a low weight. The significant advantage is, however, the possibility of producing the entire semiconductor component by deposition of the layers from solution on a polymer substrate at atmospheric pressure and temperature, for example by printing techniques, such that inexpensively producible FETs are obtained.
The performance of the electronic devices depends essentially on the mobility of the charge carriers in the semiconductor material and the ratio between the current in the on-state and the off-state (on/off ratio). An ideal semiconductor therefore has a minimum conductivity in the switched-off state and a maximum charge carrier mobility in the switched-on state (mobility above 10−3 cm2 V−1 s−1 on/off ratio above 102). In addition, the semiconductor material has to be relatively stable to oxidation, i.e. has to have a sufficiently high ionization potential, since its oxidative degradation reduces the performance of the component.
EP 1 510 535 A1 describes polythieno(2,3-b)thiophenes which have a mobility of 3·10−3 or 1.7·10−2 cm2 V−1 s−1 and on/off ratios of about 106. WO2006/094645 A1 describes polymers which have one or more selenophene-2,5-diyl and one or more thiophene-2,5-diyl groups, while WO 2006/131185 discloses polythieno(3,4-d)thiazoles, and US 2005/0082525 A1 discloses benzo(1,2-b,4,5-b′)dithiophenes.
WO2007/105386 discloses homo- and copolymers of substituted benzo[2,1-b;3,4-b′]dithiophene having the following repeating units:
and having weight average molecular weights of up to 105 g/mol. Both reported materials show charge carrier mobilities in the range of 10−5 to 10−3 cm2/Vs.
Furthermore a copolymer with bisthiophene
was reported which had only a weight average molecular weight of 4100 g/mol. This material showed only very poor performance in a field effect transistor (mobility: 1.6×10−5, on/off ratio: 100).
It is an object of the present invention to provide novel compounds for use as organic semiconductor materials, which are easy to synthesize, have high mobilities, a good stability, and can be processed readily.